The present invention relates to hydraulic systems, more particularly, the present invention relates to measuring the position of a piston in a hydraulic cylinder.
Hydraulic cylinder, piston and rod combinations, or hydraulic actuators, are used in a wide variety of industries ranging from road construction to sanitation process control. For many applications, it would be useful to know the piston position. By knowing the piston position, the location or orientation of the object being actuated by hydraulic actuators can be determined. Thus, for example, the position of a blade of a road grading machine that is actuated by one or more hydraulic actuators can be determined as a function of the piston positions of the hydraulic actuators. Furthermore, knowledge of the piston position would allow a control system to control the piston position. For example, a blade of a road grading machine could be repeatedly positioned as desired resulting in more precise grading. Other process applications include hydraulic cylinders used to move agitators or equipment used with tanks, hoppers or other components of processing plants.
One technique of determining the piston position is described in U.S. Pat. No. 4,588,953 which correlates resonances of electromagnetic waves in a cavity formed between the closed end of the hydraulic cylinder and the piston with the position of the piston within the hydraulic cylinder. Another technique uses sensors positioned within the hydraulic cylinder to sense the position of the piston. Still another technique involves attaching a cord carried on a spool to the piston where the rotation of the spool relates to piston position. However, there is an ongoing need for accurate, repeatable and reliable piston position measurement.
A measuring device is provided for determining a position of a piston contained within a hydraulic actuator as a function of a hydraulic fluid flow. The measuring device includes a bi-directional flow sensor positioned inline with the hydraulic fluid flow and a piston position module. The flow sensor is configured to produce a flow rate signal that is indicative of the direction and flow rate of the hydraulic fluid flow into a first cavity. The piston position module is configured to receive the flow rate signal from the flow sensor and produce a piston position signal as a function of the flow rate signal.